I've had one slave decide to quit talking to the other six slaves although
it and the master continue to communicate fine. And the master continues to
communicate with the six other slaves as well and they with it.

What would keep one slave that had been working fine cause it to start not
communicating with the other slaves?

This one has me stumped although the trouble seems to begin when our router
for that building had to be replaced and we replaced it with an old router
that had been used in a different building although the necessary config
files were supposedly transferred to it.

Thanks for any help, suggestions, ideas,